#include <type_traits>
#include<iostream>
int main(){
  using namespace std;
  cout<<boolalpha;
  cout<<is_reference<int>::value<<"\n";//false
  cout<<is_reference<int&>::value<<"\n";//true
  cout<<is_reference<int&&>::value<<"\n";//true
  cout<<is_reference<const int&>::value<<"\n";//true
}
